MUSCLES OF THE SHOULDER JOINT

Question 1

MUSCLES OF THE SHOULDER JOINT

Answer 1

As a result of thoracic limb’s limited function (i.e. support, flexion and extension), the mobility of the shoulder joint has been reduced; although morphologically a spheroid joint, it functions as a Ginglymus. The joint’s primary role is as a shock absorber; extension of the limb is a secondary role. The muscles of the shoulder joint take origin laterally and medially on the scapula and insert on the proximal humerus.

Question 2

M. deltoideus

Answer 2

This flat muscle lies directly under the skin, extending from the spine of the scapula to the deltoid tuberosity of the humerus. The muscle is divided into scapular and acromial parts (a clavicular part was appropriated by the M. cleidocephalicus during evolution and now forms the
M. cleidobrachialis).

Question 3

M. deltoideus origin?

Answer 3

Pars scapularis: By means of a broad aponeurosis from the spine of the scapula
and the underlying M. infraspinatus. The origin from the surface of the
infraspinous muscle gives the erroneous impression that the infraspinatus and the
scapular part of the deltoid are one muscle.
Pars acromialis: The Proc. hamatus of the Acromion (scapular spine).

Question 4

M. deltoideus insertion?

Answer 4

Tuberositas deltoidea of the humerus.

Question 5

M. deltoideus function?

Answer 5

Flexion of the shoulder joint.

Question 6

M. teres minor

Answer 6

This small, fusiform muscle is covered by the M. deltoideus.

Question 7

M. teres minor origin insertion and function?

Answer 7

Origin: Tub. infraglenoidale and distal caudal margin of the scapula.
Insertion: Tuberositas teres minor on the Linea m. tricipitis of the humerus.
Function: Flexion of the shoulder joint.

Question 8

M. infraspinatus

Answer 8

This strong muscle is largely covered by the scapular part of the M. deltoideus and its
aponeurosis.

Question 9

M. infraspinatus origin?

Answer 9

Fossa infraspinata of the scapula

Question 10

M. infraspinatus insertion?

Answer 10

Facies m. infraspinati of the humerus. The Bursa subtendinea m. infraspinati, lies beneath the tendon where it passes over the Tub. majus. Inflammation of the bursa is painful and the animal will stand with the affected limb abducted at the shoulder to relieve the tension on the tendon

Question 11

M. infraspinatus function?

Answer 11

Flexion or extension of the shoulder joint; abduction and outward rotation of the humerus. The tendon of insertion stabilizes the shoulder joint by acting as a lateral collateral ligament.

Question 12

M. supraspinatus

Answer 12

This powerful muscle occupies the supraspinous fossa. It bulges beyond the scapula’s distal
cranial margin and neck, and can be seen from the Facies costalis. The very strong tendon of
insertion also acts as a lateral collateral ligament of the shoulder joint.

Question 13

M. supraspinatus origin insertion and function?

Answer 13

Origin: Fossa supraspinata of the scapula.
Insertion: Tub. majus of the humerus.
Function: Extension and stabilization of the shoulder joint

Question 14

M. coracobrachialis

Answer 14

The tendon of origin of this short thick muscle is unusually long.

Question 15

M. coracobrachialis origin?

Answer 15

Proc. coracoideus of the scapula. The tendon runs over the medial surface of the shoulder joint where it is surrounded by a synovial sheath

Question 16

M. coracobrachialis insertion?

Answer 16

Distal portion of the Crista tuberculi minoris, caudal to the origin of the triceps’
medial head.

Question 17

M. coracobrachialis fuction?

Answer 17

Adduction and extension of the shoulder joint.

Question 18

M. subscapularis

Answer 18

The broad, flat body of this muscle contains many connective tissue septae; the muscle
is also covered by a shiny tendinous sheet. Proximal to the shoulder joint, the muscle bulges
beyond the cranial and caudal borders of the scapula. The very strong tendon of insertion serves
as a medial collateral ligament for the shoulder joint

Question 19

M. subscapularis origin insertion and function?

Answer 19

Origin: Fossa subscapularis.
Insertion: Tub. minus of the humerus.
Function: Flexion, extension, adduction and stabilization of the shoulder joint.

Question 20

M. teres major

Answer 20

This well-developed, fleshy muscle lies against the medial surface of the M. triceps brachii.

Question 21

M. teres major origin?

Answer 21

Origin: Caudal angle and proximal caudal margin of the scapula

Question 22

M. teres major insertion?

Answer 22

Insertion: Tuberositas teres major, together with the M. latissimus dorsi and M. cutaneus trunci.

Question 23

M. teres major function?

Answer 23

Flexion of the shoulder joint.

Question 24

Remarks

Answer 24

The muscles that run over the shoulder joint generally do not perform any exclusive functions. However, the two teres muscles and the deltoideus do form a distinct group: they span the caudal aspect of the shoulder and have the same innervation. The three muscles are referred to as the true flexors of the shoulder joint as they cannot exert any other influence.